Linear theory indicates that the time averaged Northern Hemisphere wintertime subtropical jet should act as a waveguide to barotropic disturbances with low-frequencies. It is expected to meridionally confine such anomalies and guide them so that their group velocity has a predominantly zonal component. By this action, the mean jet should make it possible for widely separated locations in the Northern Hemisphere to communicate with each other on seasonal timescales.

Analysis of interannual internal variability in nature and in general circulation models indicates that the predicted waveguiding influence of the mean subtropical jet does occur. Fields at widely separated locations do significantly covary provided the locations are within the confines of the mean jet. For certain variables at special longitudes correlations as large as 0.5 are achieved between points that are as much as 150 degrees of longitude occurs. By contrast conventional teleconnection patterns have marked meridional structure and widths no greater than 100 degrees.

To study the role that the waveguide can play in determining the midlatitude response to tropical heating, a sequence of general circulation model experiments is examined in which steady tropical heat sources are placed at various longitudes. These experiments indicate that regions as far away as the western Indian Ocean can affect North America as a result of the waveguide, while heating near the dateline tends to excite a circumhemispheric zonal wave five chain of circulation anomalies that are trapped in the mean jet. Analysis of observations suggests that this circumhemispheric chain sometimes makes significant contributions to the midlatitude flow pattern associated with El Nino events depending on the exact placement of the near-equator heating induced by El Nino tropical SSTs. Differences as small as 15 degrees in heating position can determine whether circumhemispheric responses do or do not occur.

Mechanisms, in addition to waveguide focussing, that contribute to formation of the remote teleconnections, including transient eddy fluxes, stationary nonlinearities, and diabatic feedbacks are diagnosed.